2-arylnaphthoxazole-derived palladium(II) complexes as phosphine-free catalysts for Heck reactions

Four air-and moisture-stable new palladium(II) complexes 2a-2c and 4 have been synthesized from easily available 2-aryinaphthoxazole derivatives. The detailed structures of 2c and 4 have been determined by single-crystal X-ray analysis. The Pd-N, Pd-C bonds in palladacycle complexes 2a-2c and the Pd-N, Pd-O bonds in complex 4 form the basis for five- and six-membered chelate rings, respectively. These complexes were applied as efficient phosphine-free catalysts for Heck reactions with aryl bromides and ethyl acrylate. Typically, in the presence of two equivalent n-Bu(4)NB3r, using 0.01% of palladacycle complex 2c as catalyst and two equivalent of K2CO3 as base in DMF at 140 degrees C provided coupled products in moderate to high yields. (c) 2007 Published by Elsevier Ltd.